In FIG. 1, an opposed-piston, opposed-cylinder (OPOC) engine 10 is shown isometrically. An intake piston 12 and an exhaust piston 14 reciprocate within each of first and second cylinders (cylinders not shown to facilitate viewing pistons). The inner pistons 12′ and 14 couple to a journal (not visible) of crankshaft 20 via pushrods 16. The outer pistons 12 and 14′ couple to two journals (not visible) of crankshaft 20 via pullrods 18, with each outerpiston 12 having two pullrods 18. The first and second cylinders in which the pistons reciprocate are parallel but offset from each other in the y direction due to the pullrods 18 associated with the cylinder shown front and leftward displaced in a negative Y direction with respect to pullrods 18 associated with the cylinder shown rear and rightward. Pushrods 16 are similarly situated with respect to each other. It is cost effective that all four pullrods 18 are identical in design and the two pushrods 16 are the same such as the design shown in FIG. 1. However, a disadvantage of such an offset design is that the engine is wider than it would otherwise be if the two cylinders could be arranged collinearly. Also, a torque is introduced due to the offset of the two cylinders. The combustion chamber shape 24 is shown on the tops of exhaust pistons 14 and 14′ and the combustion chamber shape 22 on the top of intake pistons 12 and 12′ is not visible in FIG. 1. It is desirable to minimize the number of unique parts in an assembly, but unfortunately the configuration in FIG. 1 includes four different pistons: 12, 12′, 14, and 14′.
One alternative to overcome the offset cylinders is a forked rod, such as is described in U.S. Pat. No. 1,322,824, invented by F. Royce. By employing a forked rod/blade rod configuration within the engine of FIG. 1, the cylinders are collinear, but the length of the journal (or crank pin) is greater than the configuration in which the cranks are side by side. The goal of reducing the width of the engine by making the cylinders collinear is offset by the wider crank pin lengths. A disadvantage of such a configuration is that the piston in one cylinder couples with the crankshaft by a forked rod and the corresponding piston in the other cylinder couples with the crankshaft by a blade rod thereby increasing part count for the engine. A system for coupling the rods to the crankshaft is desired which allows common parts to be used in the two cylinders, while allowing collinear cylinders and facilitating a shorter crank pin length.